Access network selection in a multi-access network environment

ABSTRACT

Novel techniques of access network selection in multi-access network environment are provided, which allow for avoiding access selection loops for independent access selection processes. The multi-access network environment provides a first access selection function, e.g. a 3GPP access selection function, and a second access selection function, e.g. an ANDSF based access selection function. At least a portion of the first access selection function may be implemented by a network component. At least a portion of the second access selection function may be implemented by a user equipment, e.g. a mobile terminal. According to the proposed concepts, a selection priority information of the first access selection function is made available to the second access selection function.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/937,780, which was filed on Jan. 5, 2011, which is anational stage application of PCT/EP2008/004792, filed Jun. 13, 2008,and claims benefit of U.S. Provisional Application 61/045,992, filedApr. 18, 2008, the disclosures of each of which are incorporated hereinby reference in their entirety.

TECHNICAL FIELD

The present invention relates to access network selection in amulti-access network environment with a plurality of access networks,the plurality of access networks comprising a first subgroup of accessnetworks, e.g. 3GPP access networks (3GPP: third generation partnershipproject), and a second subgroup of access networks, e.g. Non-3GPP accessnetworks. In particular, the present invention relates to techniques forpreventing access selection loops which may occur for independent accessselection processes.

BACKGROUND

Access technologies of various kinds, especially wireless, are becomingincreasingly ubiquitous, e.g. in the shape of GSM (Global System forMobile communication)/GPRS (General Packet Radio Service)/EDGE (EnhancedData rates for GSM Evolution), WCDMA (Wideband Code Division MultipleAccess)/HSPA (High Speed Packet Access), CDMA2000 (a cellular networkstandard based on Code Division Multiple Access), WLAN (Wireless LocalArea Network), WiMAX (Worldwide Interoperability for Microwave Access)and soon LTE (Long Term Evolution). The mobile terminals or other typesof user equipment (UE) match this multitude of access technologies byincluding ever more access interfaces to allow greater freedom andflexibility in the selection of access to use for each communicationsession.

To leverage the benefits of this growing flexibility it becomesimportant to have mechanisms in place for efficient control of theaccess selection, to ensure that a mobile node always uses its availableaccess interfaces and access networks as efficiently as possible for thecurrently ongoing communication sessions. Circumstances to be taken intoaccount include, e.g., the currently used applications, access networktechnologies and their properties, access network operators (and theirrelations to the user's home operator and/or the user), current networkconditions (e.g. load), location, subscription restrictions, time ofday, etc. Similarly, it is desirable to support a mobile node indiscovering available accesses without requiring the mobile node tocontinuously scan for all accesses and thus using battery resources.

In SAE (System Architecture Evolution)/LTE, also known as EPS (EvolvedPacket System), i.e. the future evolved 3GPP system, multi-access is akey element. Control of access selection (and access discovery) isrecognized as an important aspect and has been assigned a dedicated workitem in the 3GPP standardization process.

The mechanisms considered are based on policies and/or rules. Thefunctionality provided by a policy/rule is instructions or guidance ofwhich access to select or how to discover accesses given the specificcircumstances (device context). A policy/rule typically definescontextual conditions when it applies (e.g. for a certain application,in a certain geographical region, a certain time of day and/or day ofthe week, the PLMN (Public Land Mobile Network) the UE is currentlyregistered at, e.g. a visited PLMN during roaming, etc.) and accesspreferences. The access preferences may e.g. be a prioritized list ofaccesses, an indication of a specific only access, a list of prohibitedaccesses, or some other way of expressing how preferable certainaccesses are.

There are three basic cases of access selection:

-   -   Selection between multiple 3GPP accesses, e.g. LTE, HSPA, WCDMA,        GERAN (GSM EDGE Radio Access Network), GSM. This access        selection case may also comprise the 3GPP2 (3^(rd) Generation        Partnership Project 2) access CDMA2000, but for simplicity it is        referred to as “intra-3GPP access selection” or simply “3GPP        access selection”.    -   Selection between 3GPP and non-3GPP access(es) (where non-3GPP        accesses include e.g. WiMAX and WLAN). This access selection        case is referred to as “extra-3GPP access selection”.    -   Selection between multiple non-3GPP accesses. This access        selection case is referred to as “non-3GPP access selection”.

Extra-3GPP access selection and non-3GPP access selection are alsocollectively referred to as “ANDSF based access selection”, because, aswill be explained later, they are controlled by the functionalityprovided by the Access Network Discovery and Selection Function (ANDSF).Accordingly, in the following extra-3GPP access selection and non-3GPPaccess selection are for reasons of simplicity also collectivelyreferred to as “ANDSF based access selection”.

Policies and/or rules may be processed in the network, e.g. in the PCRF(Policy and Charging Rules Function) or, in the context of accessselection, for example in the newly introduced functional entity ANDSF,which is responsible for extra-3GPP access selection as well as non-3GPPaccess selection, i.e. access selection between 3GPP accesses andnon-3GPP accesses and between different non-3GPP accesses. The ANDSF canbe distributed between the mobile node or UE and the network. In thenetwork the ANDSF can be located both in the home network and in thevisited network. The ANDSF functionality in the UE is referred to asueANDSF, the ANDSF functionality in the home network is referred to ashANDSF, and the ANDSF functionality in the visited network is referredto as vANDSF. The network ANDSF can be located in an entity inside (i.e.as an integral part of) or can be associated with the PCRF. It is alsopossible that there will be ANDSF related functionality in non-3GPPaccess networks, e.g. for provision of access properties as input datato the access selection process. Such possible ANDSF relatedfunctionality in non-3GPP access networks is herein tentatively labeledn3aANDSF. Further information on the introduction of the ANDSF in the3GPP SAE architecture, as well as the related information flows, can,e.g. be found in “3GPP TS 23.402 v8.1.1, ‘3rd Generation PartnershipProject; Technical Specification Group Services and System Aspects;Architecture enhancements for non-3GPP accesses (Release 8)’, March2008”.

For 3GPP access selection, i.e. selection between different 3GPPaccesses that interwork on radio access network (RAN) level (such asLTE, WCDMA/HSPA and GERAN, and possibly the 3GPP2 access CDMA2000), theaccess selection functionality is separate from the ANDSF. This accessselection function is network based and is typically located within theRANs, e.g. E-UTRAN (Evolved Universal Terrestrial Radio Access Network),GERAN, UTRAN (Universal Terrestrial Radio Access Network), CDMA2000-RAN,and possibly partly also in the MME (Mobility Management Entity) and/orSGSN (Serving GPRS Support Node). Potentially, processing of accessselection related policies and rules may take place also in this accessselection function.

The ways the 3GPP access selection functionality controls the accessselection of the UEs differ between connected-mode and idle-mode UEs.Here, “connected-mode UEs” refers to UEs in connected mode, which have asignaling connection established to a RAN.

Access selection for connected-mode UEs is manifested as handoversbetween different accesses. This is, e.g., explained in “3GPP TS 36.300v8.4.0, ‘3rd Generation Partnership Project; Technical SpecificationGroup Radio Access Network; Evolved Universal Terrestrial Radio Access(E-UTRA) and Evolved Universal Terrestrial Radio Access Network(E-UTRAN); Overall description; Stage 2 (Release 8)’, March 2008” and in“3GPP TS 36.331 v8.1.0, ‘3rd Generation Partnership Project; TechnicalSpecification Group Radio Access Network; Evolved Universal TerrestrialRadio Access (E-UTRA) Radio Resource Control (RRC); Protocolspecification (Release 8)’, March 2008”. The handovers are networkcontrolled, but aided by measurement reports (e.g. received signal powerfrom neighbor cells) from the UEs. The network sets the trigger criteriafor the UEs' measurement reports (through broadcasting of thresholdsand/or by sending UE specific criteria to individual UEs) and alsodetermines when and to which cell (and access network) a handover shouldbe performed.

For idle-mode UEs access selection is realized as cell reselection, i.e.repeatedly evaluating the best cell to camp on, as well as accesstechnology (or Radio Access Technology, RAT) selection. This is, e.g.,explained in “3GPP TS 36.304 v.8.1.0, ‘3rd Generation PartnershipProject; Technical Specification Group Radio Access Network; EvolvedUniversal Terrestrial Radio Access (E-UTRA); User Equipment (UE)procedures in idle mode (Release 8)’, March 2008”. The networkbroadcasts (in the system information) the signal strength thresholdlevels determining when the UEs should evaluate neighbor cells for cellreselection. The network can also provide RAT and carrier frequencypriorities in the broadcast system information and optionally in a UEspecific signaling message when the RRC (Radio Resource Control)connection to the RAN is released.

For initial selection of PLMN and preferred access technology, e.g. whenthe UE is powered on, the UE is typically guided by information storedon the SIM card (SIM: Subscriber Identity Module) or USIM card (USIM:Universal Subscriber Identity Module). This is, e.g., explained in “3GPPTS 36.304 v.8.1.0, ‘3rd Generation Partnership Project; TechnicalSpecification Group Radio Access Network; Evolved Universal TerrestrialRadio Access (E-UTRA); User Equipment (UE) procedures in idle mode(Release 8)’, March 2008” and in “3GPP TS 23.122 v8.1.1, ‘3rd GenerationPartnership Project; Technical Specification Group Core Network andTerminals; Non-Access-Stratum (NAS) functions related to Mobile Station(MS) in idle mode (Release 8)’, March 2008”). This information originatefrom the operator (i.e. the operator with which the SIM/USIM card isassociated), but may be complemented with information from the user. Theuser can also choose to make the initial selection purely manual.

An advantage of keeping the 3GPP access selection functionality distinctfrom the ANDSF based access selection functionality is that bothselection functionalities can be optimized in this way for differenttime scales and/or interfaces. As an example, ANDSF communication maytake place on a long time scale, possibly minutes, hours or even months.Thus updates of the rules can be comparatively seldom and may betransported easily by the IP protocol. In contrast, 3GPP accessselection may be optimized for a synchronization of communications basedon timeslots of the access systems, typically on the order of severalmilliseconds. In this way, a UE can for example perform measurements onone access systems during short intervals in a transmission over adifferent 3GPP access system. This allows the preparation ofinter-system handovers even for a UE with only a single transceiver butrequires elaborate interfaces.

Access selection and access discovery are not restricted to mobile orwireless nodes/terminals. They are equally applicable for so called“user networks”. The term user network (UN) refers to one or moreinter-connected user devices that can access a network via one or moreaccess technologies. Examples of a single-device user network are acellular phone or a laptop, while an example of a multi-device usernetwork is a Personal Area Network (PAN). Although only the term UE willhenceforth be used in this document, it should be interpreted as eithera single device, i.e. a mobile terminal, or a multi-device user network.

The problem with the existing solution is that because the two accessselection mechanisms are separate, access selection loops may occur insome situations. To illustrate this problem consider the followingexample.

In a certain situation (defined by context parameters, e.g. activeapplications, time of day, etc.) the 3GPP access selection functionalityhas the following prioritized access preference list (most preferredfirst):

1. WCDMA

2. LTE

3. GERAN

Reasons for this priority order may include policies for load balancingor steering of certain applications to certain access networks (e.g.running voice calls over circuit switched WCDMA bearers).

In the same situation the ANDSF based access selection functionality hasthe following prioritized access preference list (most preferred first):

1. Corporate WLAN

2. 3GPP domain if 3GPP access=LTE is available

3. WiMAX

4. 3GPP domain if 3GPP access=WCDMA or GERAN is available

Initially we assume that the concerned UE is connected to the 3GPPdomain. Within the 3GPP domain the 3GPP access selection mechanismdirects the UE to WCDMA (even if LTE is available in the currentlocation), because this is the highest priority 3GPP access (in thegiven situation).

The UE detects an available WiMAX access and the ANDSF based accessselection mechanism determines to leave the 3GPP domain and hands overthe UE to the WiMAX access, because it has a higher priority than a 3GPPdomain represented by WCDMA.

While the UE is connected to WiMAX it scans for higher priority accessnetworks. It detects LTE but no corporate WLAN and thus, in accordancewith its prioritized access preference list, the ANDSF based accessselection functionality hands over the UE to LTE in the 3GPP domain.

Once connected to the 3GPP domain the above described mechanisms used bythe 3GPP access selection functionality kicks in and directs the UE toWCDMA, thereby forming a potentially endless access selection loop.

Accordingly, there exists a need to provide improved techniques foraccess network selection in a multi-access network environment whichprovides multiple independent access selection processes.

SUMMARY

According to an embodiment of the invention, a method of access networkselection in a multi-access network environment with a plurality ofaccess networks is provided. The plurality of access networks comprise afirst subgroup of access networks and a second subgroup of accessnetworks which are not part of the first subgroup of access networks.For example, the first subgroup of access networks may comprise 3GPPaccess networks, and the second subgroup of access networks may comprisenon-3GPP access networks, e.g. WLAN access networks or WiMAX accessnetworks. In the multi-access network environment, at least a firstaccess selection function and a second access selection function areprovided. The first access selection function is adapted to select anaccess network from the first subgroup on the basis of a first set ofselection rules, and the second access selection function is adapted toselect at least one access network from both the first subgroup and thesecond subgroup on the basis of a second set of selection rules. Thesecond selection function may select only one access network from thefirst subgroup or may select a group of access networks from the firstsubgroup, e.g. all access networks of the first subgroup. The firstaccess selection function may be a 3GPP access selection function, e.g.as described in the above-mentioned 3GPP technical specifications. Thesecond access selection function may be an ANDSF based access selectionfunction as defined above.

According to the embodiment, the method of access network selectioncomprises the step of making a selection priority information of thefirst access selection function available to the second access selectionfunction. For example, this may involve transmitting a result of thefirst access selection function from an entity implementing at least apart of the first access selection function to an entity implementing atleast a part of the second access selection function. The first accessselection function may be distributed between functional entities on thenetwork side, e.g. network components, and a user equipment. Similarly,the second access selection function may be distributed betweenfunctional entities on the network side, e.g. network components, and auser equipment. According to an embodiment, at least the finalprocessing of the second access selection function is implemented withina user equipment. The selection priority information may be stored in amemory, e.g. an access preference cache of the user equipment.

By making the selection priority information of the first accessselection function available to the second access selection function,the second access selection function becomes aware of the preferences ofthe first access selection function, which allows for avoiding undesiredaccess selection loops.

According to an embodiment, in the second access selection function anaccess network from the first subgroup is only selected, i.e. consideredfor selection, if no other access network of the first subgroup having ahigher priority according to the first set of selection rules isavailable. In this way, the selection priority information of the firstaccess selection function is taken into account in the second accessselection function, and the second access selection function will selectthat access network of the first subgroup which would also be selectedaccording to the first access selection function.

The selection priority information may specify an access network of thefirst subgroup which is selected according to the first access selectionfunction, and in the second access selection function those accessnetworks of the first subgroup which have lower priority than theselected access network of the first access selection function may befiltered out. For example, the second access selection function may usea list of access networks with associated priorities. In this case, thelist can be filtered according to the first selection rules so that onlythe access network from the first subgroup with the highest priorityremains in the list apart from the access networks of the secondsubgroup.

According to an embodiment, the method may also involve maintaining anavailability information indicating which access networks of the firstsubgroup are available for a particular user equipment. Further, theselection priority information may be generated on the basis of anaccess network of the first subgroup which is used by a particular userequipment when the user equipment changes to an access network of thesecond subgroup. The selection priority information may also begenerated on the basis of those access networks of the first subgroupwhich are available for a particular user equipment when the userequipment changes to an access network of the second subgroup. Inaddition, it is also possible to generate the selection priorityinformation on the basis of contextual parameters which are valid for aparticular user equipment when the user equipment changes to an accessnetwork of the second subgroup. The contextual parameters may beselected from the group comprising: an information on activeapplications of the user equipment, an information on the location ofthe user equipment, an information on the velocity of the userequipment, an information on the time of day, an information on the dayof the week, and an information on a PLMN the user equipment iscurrently registered at. That is to say, the selection priorityinformation may not only be generated by directly transmitting a resultof the first access selection function to the second access selectionfunction, but may also be accomplished by monitoring parameters, e.g.access selection results, related to the first access selectionfunction, which allow for making a conclusion on a preferred accessnetwork of the first access selection function.

According to a further embodiment, a network component for use in theabove-described type of multi-access network environment is provided. Inaccordance with the above-described concepts, the network component isadapted to make a selection priority information of the first accessselection function available to the second access selection function.The network component may be a functional entity which is typically usedto implement the ANDSF functionality in the home network or in thevisited network, e.g. the hPCRF (home PCRF, the PCRF in the homenetwork) or the vPCRF (visited PCRF, the PCRF in the visited network).These functional entities are explained in the 3GPP technicalspecifications. Accordingly, the network component may be configured toimplement at least a portion of the second access selection function.Preferably, the network component is configured to operate according tothe above-described methods.

According to a further embodiment of the invention, a user equipment foruse in the above-described multi-access network environment is provided.The user equipment may be a mobile terminal or mobile node, e.g. acellular phone. However, it may also be a user network comprising one ormore inter-connected user devices that can access a network via one ormore access technologies. The user network may be of the single-devicetype, e.g. a cellular phone or a laptop, or of a multi-device type, e.g.a PAN (Personal Area Network).

According to the embodiment, the user equipment is adapted to make aselection priority information of the first access selection functionavailable to the second access selection function. At least a portion ofthe second access selection function may be implemented by the userequipment, e.g. by the ueANDSF.

The user equipment may be provided with a cache memory for storing theselection priority information of the first access selection function.Further, the user equipment may be provided with functional entities formonitoring parameters related to the first access selection function.The selection priority information may then be generated on the basis ofthe monitored parameters. The user equipment may also directly receivethe selection priority information from a functional entity implementingat least a portion of the first access selection function, e.g. from anetwork component.

The user equipment is preferably configured to operate according to theabove-described methods.

According to a further embodiment of the invention, a network system foruse in the above-described multi-access environment is provided. Thenetwork system comprises at least one network component which implementsat least a portion of the first access selection function, and a userequipment and/or a further network component which implements at least aportion of the second access selection function. The network system isadapted to make a selection priority information of the first accessselection function available to the second access selection function,e.g. by transmitting corresponding data from the at least one networkcomponent to the user equipment and/or to the further network component.The network system is preferably configured to operate according to theabove-described methods.

The concepts of the present invention may be implemented by softwarerunning on a computer system. In particular, the user equipment may beimplemented as a computer system comprising a computer processor and amemory storing a program code, and the program code may be configured insuch a way that the user equipment operates according to theabove-described methods and concepts. Accordingly, an embodiment of thepresent invention provides a computer program product comprising aprogram code for performing the above-described method when the programcode is executed on a computer system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B and 1C schematically illustrate different scenarios ofaccess network selection which may occur in a multi-access networkenvironment as used according to embodiments of the invention.

FIG. 2 schematically illustrates the ANDSF in the 3GPP SAE architectureand the most basic related information flows.

FIG. 3 schematically illustrates an exemplary ANDSF based multi-accesspolicy and rule control architecture as used according to an embodimentof the present invention.

FIG. 4 schematically illustrates the SAE architecture with the accessselection functionality for selecting between accesses interworking onRAN level as used according to embodiments of the invention.

FIG. 5 schematically illustrates a network system according to anembodiment of the invention.

FIG. 6 schematically illustrates an exemplary procedure for 3GPP accessselection according to an embodiment of the invention.

FIG. 7 schematically illustrates an exemplary procedure for ANDSF basedaccess selection according to an embodiment of the invention.

FIG. 8 schematically illustrates an exemplary procedure for ANDSF basedaccess selection according to an embodiment of the invention, which isaware of the 3GPP access selection preference.

FIG. 9 schematically illustrates a network system according to a furtherembodiment of the invention.

DETAILED DESCRIPTION

In the following, the invention will be explained in more detail byreferring to exemplary embodiments which relate to a typicalmulti-access environment in accordance with the 3GPP above-mentionedtechnical specifications. The multi-access network environment comprisesa plurality of access networks which may be classified in a firstsubgroup of 3GPP access networks and a second subgroup of non-3GPPnetworks. Two distinct access selection functions are provided, a firstaccess selection function being adapted to select an access network fromthe first subgroup and the second access selection function beingadapted to select an access network from both the first subgroup and thesecond subgroup. The first access selection function is referred to as3GPP access selection functionality, and the second access selectionfunction is referred to as ANDSF based access selection functionality.However, it is to be understood that the ANDSF based access selectionfunctionality of this application does not need to be a function asdefined in the 3GPP specifications. Rather, it can also be any accessselection function for selecting between detected accesses, whichconsiders at least one access which can also be selected by anotheraccess selection function.

As mentioned above, according to some embodiments of the invention, thefirst subgroup of access networks is formed of 3GPP access networks, andthe second subgroup of access networks is formed of non-3GPP accessnetworks. In this case, the first access selection function is a 3GPPaccess selection functionality, and the second access selection functionis an ANDSF based selection functionality. According to the aboveconcepts, the distinct separation of the two access selection mechanismsare retained, but the ANDSF based access selection functionality infersthe preferences of the 3GPP access selection functionality, either bylearning the (3GPP) RAT/frequency selection priorities provided to theUE, or by observing which of the available 3GPP access that is beingused when the UE is associated to the 3GPP domain. In this context,“associated” means that the 3GPP access selection function can presentlyselect a 3GPP access for the UE. In particular, the association can be aconnection in connected-mode, or an association in idle-mode (i.e.camping).

Based on its observations of the 3GPP access selection functionality theANDSF based access selection functionality can conclude that the 3GPPaccess selection functionality prefers a certain 3GPP access to one ormore other 3GPP accesses. However, the ANDSF access selectionfunctionality can only assume that its conclusion is valid as long as nosignificant change occurs in the relevant contextual parameters (whichcan consist e.g. of the currently actively communicating application(s),or signal strength and/or availability). Thus, when the UE is handedover from the 3GPP domain to a non-3GPP access the ANDSF based accessselection functionality temporarily stores its conclusion in a 3GPPaccess preference cache and keeps it there until it either times out ora relevant change occurs in the relevant contextual parameters.

As long as a 3GPP access preference conclusion is stored in the 3GPPaccess preference cache the ANDSF based access selection functionalitycan use it as a guideline (in addition to its regular policies/rules)when considering handing over the UE to a 3GPP access. This means thatthe ANDSF based access selection functionality will not hand over the UEto a 3GPP access, which according to the information in the 3GPP accesspreference cache is not the most preferred of the currently available3GPP accesses. Yet a consequence is that if the one of the available3GPP accesses that is the most preferred according to the 3GPP accesspreference cache does not have a higher priority (in the view of theANDSF based access selection functionality) than the currently usednon-3GPP access, the ANDSF based access selection functionality will nothand over the UE to the 3GPP domain.

In some embodiments the ANDSF based access selection functionality has adistinct notion of which 3GPP accesses are available. This notion can bebased on explicit detections of availability and timers during periodswithout explicit confirming indications. Explicit detections ofavailability can be obtained e.g. through scanning or the presence ofactive connections or from explicit messages, for example messages fromthe ANDSF in the network, informing the ueANDSF of available accesses.Optionally inter-RAT neighbor lists provided from the RAN to which theUE is currently connected can also be used as a detection ofavailability. Here, it should be noted that accesses included inneighbor lists are not necessarily available. Inclusion in the neighborlist only indicates that they may be available and thus worth measuringon when evaluating handover candidates.

Using the solution in the example discussed in the introductory portionwould cause the UE to remain connected to WiMAX and not change to LTE,thus avoiding running into the access re-selection loop.

Accordingly, with the inventive solution access selection loopsinvolving ANDSF based and intra-3GPP access selection are avoided. Itcan be implemented with low complexity and would not add a significantprocessing load for the UE.

While the invention has been described so far specifically in a 3GPPcontext it is not limited to this scenario. As explained above, theinvention may also be applied generally to a communication system with aplurality of access networks and at least two access selectionfunctions. The plurality of access networks comprises a first subgroupof access networks and further access networks which are not part of thefirst subgroup. A first of the access selection functions is adapted toselect an access within the first subgroup according to first selectionrules. A second of the access selection functions is adapted to selectan access network from the further access networks and the firstsubgroup. The second access selection function considers in a selectionan access network from the first subgroup only if it has the highestpriority according to the first selection rules. Any embodimentsdescribed in connection with a 3GPP implementation may also be amendedto this general concept of the invention.

FIGS. 1A, 1B, and 1C schematically illustrate different scenarios ofaccess network selection which may occur in a multi-access networkenvironment of the above-mentioned type.

FIG. 1A illustrates the selection between multiple 3GPP accesses, e.g.LTE, HSPA, WCDMA, GERAN, GSM. This type of access selection may alsoinvolve the 3GPP2 access CDMA2000. As illustrated a UE 100 may selectbetween a first 3GPP access network 10A, a second 3GPP access network10B, and a third 3GPP access network 10C. That is to say, in this casethe selection occurs within a 3GPP domain 10.

FIG. 1B illustrates a selection between 3GPP and non-3GPP accesses. Thenon-3GPP accesses may include, e.g., a WiMAX access or a WLAN access. Asillustrated, the user equipment 100 may select between access networksof the 3GPP domain 10, i.e. a first 3GPP access network 10A and a second3GPP access network 10B, and non-3GPP access networks, i.e. a firstnon-3GPP access network 20A and a second non-3GPP access network 20B.

FIG. 1C illustrates the selection between multiple non-3GPP accesses. Asillustrated, the user equipment 100 may select between a first non-3GPPaccess network 20A, a second non-3GPP access network 20B, and a thirdnon-3GPP access network 20C.

The selection process of FIG. 1A is referred to as intra-3GPP accessselection or simply 3GPP access selection, the selection process of FIG.1B is referred to as extra-3GPP access selection, and the selectionprocess of FIG. 1C is referred to as non-3GPP access selection.Extra-3GPP access selection and non-3GPP access selection arecollectively referred to as the ANDSF based access selection becausethey are controlled by the functionality as provided by the ANDSF.

FIG. 2 schematically illustrates the ANDSF in the 3GPP SAE architecture,as well as the most basic related information flows. Further informationcan be obtained from the above-mentioned 3GPP technical specifications.

The architecture as illustrated in FIG. 2 comprises a HPLMN domain(HPLMN: home public land mobile network), a VPLMN domain (VPLMN: visitedpublic land mobile network), and a domain of non-3GPP networks. Thedifferent domains are separated by horizontal dashed lines.

The HPLMN domain comprises a home subscriber server (HSS) 210, a homepolicy and charging rules function (hPCRF) 220, a packet data network(PDN) gateway 230, and a 3GPP AAA server 240 (AAA: authentication,authorization and accounting). An operator's internet protocol (IP)services are denoted by 250 and may comprise, e.g., an IP multimediasub-system (IMS), and a packet switched streaming service (PSS). TheHPLMN domain also comprises a hANDSF, denoted by 222, which may beimplemented in the hPCRF 220 or as a separate functional entity.

The VPLMN domain comprises a visited policy and charging rules function(vPCRF) 260, an evolved packet data gateway (ePDG) 265, a 3GPP access270 with a serving gateway 275, and a 3GPP AAA proxy 280. The VPLMNdomain also comprises a vANDSF, denoted by 262, which may be implementedin the vPCRF 260 or as a separate functional entity.

The domain of non-3GPP networks comprises a trusted non-3GPP access 290and an untrusted non-3GPP access 295, optionally provided with ann3aANDSF 292 and 297, respectively.

Finally, FIG. 2 also illustrates the UE 100 which is provided with aueANDSF 110.

The illustrated entities and components communicate via reference pointsor signal interfaces, denoted by S1, S2a, S2b, S6, S6a, S7, S7a, S7b,S7c, S8a/b, S9, S14, S15, SGi, Ta*, rx+, Wa*, Wd*, Wm*, Wx*. These arefurther explained in the above-mentioned 3GPP technical specifications.

Processing of policies and/or rules in the ANDSF may take place eitherin the network, in the UE 100 or in both. In one scenario at least thefinal processing will take place in the UE 100 where the accessselection decision is executed. The UE 100 communicates with the hANDSF222, e.g. to receive policy and rule information. The vANDSF 262 and thehANDSF 222 may also communicate such information between each other, buta possible alternative is that the UE 100 communicates directly with thevANDSF 262. Note, however, that different implementations are possibleand for example the vANDSF 262 or the n3aANDSF 292, 297 could beomitted.

The ANDSF based access selection functionality can execute its accessselection decision as an IP mobility mechanism. The IP mobilitymechanism can be for example, Mobile Internet Protocol version 6(MIPv6), Proxy Mobile Internet Protocol version 6 (PMIPv6), Dual-StackMobile Internet Protocol version 6 (DSMIPv6), Mobile Internet Protocolversion 4 (MIPv4) or Proxy Mobile Internet Protocol version 4 (PMIPv4).The ANDSF based access selection functionality may also includepolicies/rules defining if and when to scan for available accessnetworks.

FIG. 3 schematically illustrates an exemplary ANDSF based multi-accesspolicy and rule control architecture.

As illustrated, the architecture comprises the multi-access UE 100, theANDSF 300, a data base 350, and an application function 360, e.g. aproxy call session control function (P-CSCF). The ANDSF may be a hANDSF,a vANDSF, or an n3aANDSF. The data base 350 stores a subscriber profile.The application function 360 provides the ANDSF 300 with applicationrequirements and indicates events. The ANDSF stores operator policyrules 320 and comprises a policy decision function 310 which makespolicy decisions based on the policy rules, the subscriber profile andthe application requirements. Based on the policy decisions,multi-access control rules/events are generated, which are supplied tothe multi-access UE 100.

The multi-access UE 100 executes an application, denoted by 120, e.g. anIMS client. The UE 100 stores local preferences and data 140 andmulti-access control rules 150 as supplied from the ANDSF 300.

An access selection and scanning control function 130 of themulti-access UE 100 makes access selection and scanning controldecisions based on the multi-access control rules and the localpreferences. In addition, the access selection and scanning controlfunction may receive data from the application 120 and may be suppliedwith local triggers, which are taken into account in the decisionprocess.

The 3GPP access selection function is implemented separately from theANDSF. This access selection function is network based and typicallylocated within the RANs, e.g. within an E-UTRAN, a GERAN, a UTRAN, aCDMA2000-RAN, and possibly partly also in the MME and/or the SGSN.

FIG. 4 schematically illustrates the SAE architecture with the 3GPPaccess selection functionality for selection between accessesinterworking on RAN level. Similar to the architecture of FIG. 2, thearchitecture comprises a HPLMN domain and a VPLMN domain, which areseparated by a horizontal dashed line. FIG. 4 illustrates a roamingscenario, where access networks in the VPLMN domain, but not in theHPLMN domain are utilized. However, it is to be understood that otherscenarios are possible in which access networks from both the VPLMNdomain and the HPLMN domain are utilized.

The HPLMN domain comprises the HSS 210, the hPCRF 220, the PDN gateway230, and the operator IP services 250.

The VPLMN domain comprises an UTRAN 410, a GERAN 420, a E-UTRAN 430, anSGSN 440, a MME 450 with corresponding access selection functionalityfor accesses interworking on RAN level, denoted by 415, 425, 435, 445,and 454, respectively. In addition, the VPLMN domain comprises theserving gateway 275.

In addition, FIG. 4 also illustrates the UE 100. For example, the UE maycommunicate with the E-UTRAN 430 using the LTE access technology.

In FIG. 4, reference points or signal interfaces for establishingcommunication between the illustrated components and entities aredenoted by S1-U, S1-MME, S3, S4, S6a, S7, S8a, S12, SGi, Rx+, and Uu.These are further explained in the 3GPP above-mentioned technicalspecifications.

In the following, a solution will be proposed which allows forpreventing access selection loops in the multi-access networkenvironment which uses the 3GPP access selection functionality and theANDSF based access selection functionality.

FIG. 5 schematically illustrates a network system which implements theproposed solution.

The network system comprises the UE 100 and a first network component560 and a second network component 570 of an operator's network 550. Thefirst network component 560 implements at least a part of the 3GPPaccess selection functionality 565, and may be part of the UTRAN, theGERAN, the E-UTRAN, the SGSN, or the MME. The second network component570 implements at least a portion of the ANDSF based access selectionfunctionality 575, in particular the hANDSF or the vANDSF. Accordingly,the second network component 570 may be implemented as a part of a hPRCFor a vPRCF, as for example illustrated in FIG. 2.

As further illustrated, the UE 100 comprises the ueANDSF and a memory520 storing a 3GPP selection priority information of the 3GPP accessselection function. The memory may also be referred to as 3GPP accesspreference cache. The 3GPP selection priority information is supplied tothe ueANDSF 110 so as to be taken into account in the ANDSF based accessselection functionality.

Note that the network system of FIG. 5 is one example and other examplesare conceivable, e.g. that the network implements the memory 520 storing3GPP access priority information (i.e. the 3GPP access preference cache)as a part of the ueANDSF.

In the proposed solution it is the task of the ANDSF based accessselection functionality to “observe” the 3GPP access selectionfunctionality and use the conclusions of its observations to avoid orbreak access selection loops. The observations consist of tracking howthe UE is directed/handed over between different 3GPP accesses. To drawappropriate and useful conclusions the ANDSF based access selectionfunctionality can also extend, or generalize, its knowledge aboutavailable accesses and/or make intelligent assumptions about them.

According to an embodiment of the invention as illustrated in FIGS. 6-8,the 3GPP accesses used in the ANDSF-based access selection scheme arereplaced with the outcome of the 3GPP access selection process. For thispurpose a 3GPP access selection procedure and an ANDSF-based accessselection procedure are coupled. FIG. 6 shows an exemplaryimplementation of the 3GPP access selection function and FIG. 7 shows anexemplary implementation of the ANDSF-based access selection function.An exemplary implementation of procedure resulting from the coupling ofthe procedures of FIGS. 6 and 7 is shown in FIG. 8.

In FIGS. 6-8, the term “RAT” refers to a combination of accesstechnology and access technology characteristics (e.g. frequencycarrier, bandwidth, version/profile, operator, etc.). The same selectionprocedures can also be used for selecting between different RANs, e.g.different WLANs

In the 3GPP access selection procedure 600 of FIG. 6, at step 605 UEcapabilities are specified. In the illustrated example, it is specifiedthat UE is capable of using the RATs x, y and z.

At step 610, a list of possible 3GPP RATs is provided, in theillustrated example RATs w, x, y, and z.

At step 612, pre-provisioned preferences are provided, and in step 614network control information for handover and cell (re-)selection isobtained.

At step 615, on the basis of the pre-provisioned preferences of step612, and on the basis of the network control information of step 614,forbidden RATs are identified.

In step 620, the list of 3GPP RATs of step 610 is supplied to a RATfilter so as to filter out the forbidden RATs of step 615. This resultsin a list of usable 3GPP RATs of step 630, in the illustrated examplethe RATs X, Y, and Z.

In step 635, the list of usable 3GPP RATs of step 630 is subjected to aRAT prioritization. This is accomplished on the basis of theprepositioned preferences of step 612 and on the basis of the networkcontrol information of step 614. The result is the 3GPP RAT preferencelist of step 640, which in the illustrated example gives the followingpriority order:

1. X

2. Y

3. Z

In step 642 access scanning is accomplished, and in step 644 locallystored and/or network provided neighbour cell information is obtained.The resulting information is used to obtain a list of available 3GPPRATs in step 650. In the illustrated example, the available 3GPP RATsare the RATs X, Y, and Z.

In step 660, the 3GPP RAT preference list of step 640 and the list ofavailable 3GPP RATs of step 650 are subjected to a RATselection/terminal steering process. The result is a selected 3GPP RATof step 665, in the illustrated example RAT X.

In step 670, the selected 3GPP RAT of step 665 is used to controlhandover or cell re-selection. For example, if the presently used 3GPPRAT does not correspond to the selected 3GPP RAT of step 665, a handoveror cell re-selection may be initiated.

In the ANDSF based access selection procedure of FIG. 7, at step 705 UEcapabilities are defined in step 705. In the illustrated example, the UEis capable of using the non-3GPP RATs A, B, C, and D. In step 710, alist of possible non-3GPP RATs is provided, in the illustrated examplenon-3GPP RATs A, B, C, D.

In step 712, pre-provisioned preferences are provided, and in step 714network control information is obtained via ANDSF policies. On the basisof the pre-provisioned preferences of step 712 and the network controlinformation of step 714, forbidden RATs are identified at step 715.

In step 720, the list of non-3GPP RATs of step 710 is supplied to a RATfilter so as to filter out the forbidden RATs of step 715. The result isthe list of usable non-3GPP RATs of step 730, which in the illustratedexample includes the non-3GPP RATs A, B, C, and D.

In step 735, the list of usable non-3GPP RATs of step 730 is subjectedto a RAT prioritization. This is accomplished on the basis of thepre-provisioned preferences of step 712 and the network controlinformation of step 714. The result is a list of 3GPP and non-3GPP RATpreference list of step 740. In the illustrated example, the listdefines the following priority order:

1. D

2. A

3. 3GPP (X)

4. B

5. 3GPP (Y)

6. 3GPP (Z)

7. C

In step 742, access scanning is accomplished, and in step 744 locallystored and/or network provided neighbour cell information is obtained.

In step 750, a list of available non-3GPP RATs is obtained on the basisof the access scanning information from step 742 and the neighbour cellinformation from step 744. In the illustrated example, the availablenon-3GPP RATs are the RATs B and C.

Similarly, in step 755, a list of available 3GPP RATs is obtained on thebasis of the access scanning information from step 742 and the neighbourcell information from step 744.

In step 760, the 3GPP and non-3GPP RAT preference list of step 740, thelist of available non-3GPP RATs of step 750, and the list of available3GPP RATs of step 755 are subjected to a RAT selection/terminal steeringprocess. The result is a selected RAT of step 765. The selection optionsare the RATs A, B, C, and D, and 3GPP. The latter option means that a3GPP RAT is selected, without specifying a specific 3GPP RAT.

In step 770, a handover or cell re-selection process is controlled onthe basis of the selected RAT of step 765.

In FIG. 8, the 3GPP access selection procedure of FIG. 6 and the ANDSFbased access selection procedure of FIG. 7 are coupled. Those stepswhich have already been explained in connection with FIG. 7 have beendesignated with the same reference signs and the repeated descriptionthereof will be omitted.

In FIG. 8, a result of the 3GPP access selection procedure 600 issupplied to the ANDSF based access selection procedure in the form of a3GPP RAT preference list or a selected 3GPP RAT, as obtained in step 640or 665 of the 3GPP access selection procedure 600.

In step 820, the 3GPP RAT preference list of selected 3GPP RAT of step810 and the list of available 3GPP RATs of step 755 are supplied to a3GPP RAT filter so as to obtain the available 3GPP RAT having thehighest priority according to the 3GPP access selection function. Thisresult is given in step 830. In the illustrated example, the preferredor selected 3GPP RAT is the RAT Y.

The preferred or selected 3GPP RAT of step 830 and the list of availablenon-3GPP RATs of step 750 are subjected to the RAT selection/terminalsteering process of step 760. The result in step 765 is a selected RAT.In the illustrated example, this is the RAT B.

As can be seen, in the procedure of FIG. 8 the ANDSF-based accessselection process does not consider all 3GPP accesses that are availablefor the UE in the access selection decision. Instead it only considersthe 3GPP access which is currently selected, or the one which ispreferred according to the 3GPP access selection process.

In particular it should be noted that the selected RAT in FIG. 7 andFIG. 8 is different. Both in FIGS. 7 and 8 RAT D and A which are thehighest entries in the ANDSF preference list are not selected becausethey were not detected as available. However, the process in FIG. 7selects then a 3GPP RAT which is the next highest entry in the ANDSFpreference list. In contrast the process in FIG. 8 detects that thepreferred or selected 3GPP RAT is RAT Y which corresponds to a lowerposition in the ANDSF preference list, here position 5, and only RAT Yis considered in the ANDSF selection process. Therefore RAT B is insteadselected in FIG. 8 because it has a higher priority than the preferredor selected 3GPP RAT.

According to a further embodiment, when an access has been detected(e.g. through scanning or other explicit indication), the ANDSF basedaccess selection functionality considers it as available for a certaintime, T_(available), without any explicit confirming indications. Thevalue of T_(available) may be access specific, e.g. greater for accesseswhich normally have large coverage areas and smaller for access typeswhich normally are short-range with spotty coverage, but it may also bethe same for all accesses. A timer is provided for measuring when thetime T_(available) has elapsed. This timer is referred to as an accessavailability timer.

In addition, an actively used access (i.e. an access which the UE isconnected to in active mode or actively communicating through) is alsoconsidered as available and its access availability timer is not starteduntil the UE disconnects from the concerned access or leaves the activemode for the access.

Furthermore, an access for which the UE detects loss of signal (e.g. LTEreference signals or WLAN beacons) or a reduction of the received signalstrength below a certain threshold (which may be access specific), theUE should interpret this as an explicit indication of unavailability andshould consider the access as unavailable irrespective of the value ofany running access availability timer for the access.

According to the embodiment, the UE may track only the availability of3GPP accesses in the manner described above. However, the same may bedone for non-3GPP accesses.

While a UE is connected to the 3GPP domain, the ANDSF based accessselection functionality learns which 3GPP access the 3GPP accessselection functionality chooses to use; this is achieved by observationof how the 3GPP accesses are used by the UE, or by receiving explicitinformation about the 3GPP access priority setting. When the UE leavesthe 3GPP domain, e.g. because it is handed over to a non-3GPP access,the ANDSF based access selection functionality notes the following:

-   -   the preferred 3GPP access for the UE (i.e. the one used before        handing over to non-3GPP);    -   the currently available 3GPP accesses; and    -   the current relevant contextual parameters.

In this context, the “relevant” contextual parameters may consist ofonly the active application(s) (i.e. the communicating application(s)),but any other contextual parameters, such as geographic location,velocity, PLMN, time of day, and/or day of the week may be included.

In a simultaneous multi-access scenario where the UE may be connected toa 3GPP access and one or more non-3GPP accesses simultaneously only theapplication(s) (or application flow(s)) communicating over the 3GPPaccess is (are) relevant and stored.

The ANDSF based access selection functionality uses the above listeddata to create a temporary entry in a cache, which is herein denoted as3GPP access preference cache. The purpose of the cache entry is torecord the conclusion that the ANDSF based access selectionfunctionality can draw from its observations. For instance, if the UEwas using 3GPP access X before it left the 3GPP domain and 3GPP accessesY and Z were also available, the ANDSF based access selectionfunctionality concludes that in the current situation (i.e. with thecurrent contextual parameters) the 3GPP access selection functionalityprefers 3GPP access X to 3GPP accesses Y and Z. This conclusion isstored in the newly created cache entry. The ANDSF based accessselection functionality may also store the available 3GPP accesses andthe current relevant contextual parameters in the cache entry, but ifany of this data is stored in other ways, where it is accessible for theANDSF based access selection functionality, it may be omitted in thecache entry.

As long as the entry is stored in the 3GPP access preference cache theANDSF based access selection functionality uses it as a guideline (inaddition to its regular policies/rules) when considering handing overthe UE to a 3GPP access. In this example this means that as long as theentry remains in the cache, the ANDSF based access selectionfunctionality will not hand over the UE to 3GPP access Y or Z if 3GPPaccess X is available—not even if any of 3GPP accesses Y or Z has ahigher priority (in the view of the ANDSF based access selectionfunctionality) than the available non-3GPP accesses. It also means thatif 3GPP access X has lower priority (in the view of the ANDSF basedaccess selection functionality) than at least one of the availablenon-3GPP accesses, the ANDSF based access selection functionality willnot hand over the UE to the 3GPP domain.

The 3GPP access preference recorded in the cache entry is not permanent.If relevant circumstances change, the 3GPP access selectionfunctionality also may change its preferences and in particular itsrelative priority order of the 3GPP accesses concerned in the cacheentry (i.e. the relative priority order of 3GPP accesses X, Y and Z inthe example). Therefore the cache entry is removed when an event occursthat is likely to impact the preferences of the 3GPP access selectionfunctionality.

Such “relevant events” include changes in the relevant contextualparameters that are stored in the 3GPP access preference cache entry (orelsewhere accessible for the ANDSF based access selectionfunctionality).

Depending on the nature of the concerned contextual parameter the ANDSFbased access selection functionality may have to use a certain margin orthreshold, which must be passed in order for the change to besignificant enough to trigger removal of a 3GPP access preference cacheentry.

As stated above, the contextual parameters typically only include theactive application(s), but may also include other parameters. Hence, ifone of the active applications is terminated or if a new one is startedor if the communication characteristics of an active application aresignificantly changed (e.g. a media component added or dropped), the3GPP access preference cache entry can be deleted depending on theparticular embodiment. Here, it should be noted that in a simultaneousmulti-access scenario where the UE may be connected to a 3GPP access andone or more non-3GPP accesses simultaneously only changes in theapplications communicating over the 3GPP access impact the 3GPPpreference cache.

The 3GPP access preference cache entry is also deleted if the ANDSFbased access selection functionality directly observes a change in thepreferences of the 3GPP access selection functionality that are recordedin the cache entry (e.g. an observation that X is no longer preferred toY and Z in the example). In the example above the ANDSF based accessselection functionality may for instance observe that the 3GPP accessselection functionality selects 3GPP access Y (instead of X) out of theavailable 3GPP accesses X, Y and Z and then the ANDSF based accessselection functionality consequently removes the 3GPP access preferencecache entry indicating that 3GPP access X is preferred over Y and Z.

In the absence of relevant events the lifetime of the created cacheentry is limited to T_(3GPP-pref-lifetime). Hence a timer, also referredto as 3GPP preference timer, is started when a 3GPP access preferencecache entry is created. If the 3GPP preference timer expires (indicatingthat the time T_(3GPP-pref-lifetime) has elapsed since the cache entrywas created), the cache entry is deleted. The 3GPP preference timer maybe restarted before it expires if the ANDSF based access selectionfunctionality observes an indication that confirms the 3GPP accesspreferences that are recorded in the cache.

A 3GPP access preference cache entry removal should preferably triggerthe ANDSF based access selection functionality to consider change ofaccess (i.e. it may now be useful to switch to the 3GPP domain so anevaluation of this is appropriate), provided that the UE is currentlyconnected to a non-3GPP access. If the cache entry removal was due to acontextual change, then the contextual change in itself is probablyenough to trigger such evaluations, but if the cache entry is timed out,the actual removal of the cache entry is the only trigger.

It should be noted that even though changes in the availability ofaccesses do not trigger removal of a 3GPP access preference cache entry,they may impact the ANDSF based access selection functionality'sdecisions whether or not to hand over a UE to the 3GPP domain. Toillustrate this, consider the following examples.

The 3GPP accesses X, Y and Z and the non-3GPP accesses A and B areavailable. The UE is connected to non-3GPP access A and the ANDSF basedaccess selection functionality has recorded in the 3GPP accesspreference cache that the 3GPP access selection functionality prefers3GPP access X to Y and Z. Furthermore, the relative priority order ofthe available accesses according to the ANDSF based access selectionfunctionality is (with highest priority listed first) Y, A, X, B, Z.

In accordance with the described solution the ANDSF based accessselection functionality does not hand over the UE to 3GPP access Y (eventhough it has higher priority than non-3GPP access A), because of therecorded information in the 3GPP access preference cache which indicatesthat the 3GPP access selection functionality would hand over the UE from3GPP access Y to X, which according to the ANDSF based access selectionfunctionality has a lower priority than the currently used non-3GPPaccess A. Nor does it hand over the UE to 3GPP access X because ANDSFbased access selection functionality prefers the currently used non-3GPPaccess A to 3GPP access X.

Assume now that non-3GPP access A becomes unavailable. The ANDSF basedaccess selection functionality then has the choice to hand over the UEeither to non-3GPP access B or to the 3GPP domain. Since 3GPP access X(which according to the 3GPP access preference cache entry will be theend result of a handover to the 3GPP domain) according to the ANDSFbased access selection functionality has higher priority than non-3GPPaccess B, the ANDSF based access selection functionality chooses to handover the UE to 3GPP access X.

Consider again the same example, but instead of non-3GPP access Abecoming unavailable the new 3GPP access Q becomes available. Accordingto the priorities of the ANDSF based access selection functionality thenew access Q has higher priority than A but lower than Y (i.e. therelative priority order of the available accesses are Y, Q, A, X, B, Zaccording to the ANDSF based access selection functionality). Sincethere is now an available 3GPP access which has a higher priority thanthe currently used non-3GPP access and which is not disqualified byinformation in the 3GPP access preference cache, the ANDSF based accessselection functionality chooses to hand over the UE to the 3GPP domain.Still it does not hand over the UE to the highest priority access Y(since this is still disqualified by the 3GPP access preference cache),but to the new 3GPP access Q.

The result would have been the same if the new 3GPP access Q insteadwould have had a higher priority than Y (i.e. if the relative priorityorder of the available accesses would have been Q, Y, A, X, B, Zaccording to the ANDSF based access selection functionality), but if Qwould have had lower priority than A, then the ANDSF based accessselection functionality would not have handed over the UE.

FIG. 9 schematically illustrates a network system which constitutes anexemplary implementation of the above-embodiment. The network systemgenerally corresponds to that of FIG. 5 and similar components aredesignated with the same reference signs.

As illustrated, the UE 100 of FIG. 5 has been replaced with a UE 100′.The UE 100′ additionally comprises a monitoring function 530, the accessavailability timer 535, and the 3GPP preference timer 525. Themonitoring function 530 accomplishes monitoring of parameters related tothe 3GPP access selection function. For example, the presently selected3GPP access, the availability of 3GPP accesses, and/or the contextualparameters may be evaluated. These are used as a basis for generatingthe 3GPP selection priority information stored in the access preferencecache.

Other exemplary implementations of the above embodiment may includevariations of the exemplary implementation of FIG. 9, e.g. that all orsome of the related functions in the UE 100′, i.e. monitoring function530, the memory 520 storing the 3GPP selection priority information(i.e. the 3GPP access preference cache), the access availability timer535 and the preference timer 525 are included in the ueANDSF 110. In yetanother exemplary implementation the access availability timer 535 andthe preference timer 525 are separate from the ueANDSF 110, butcontrolled by the ueANDSF 110.

Returning to the example of access selection loops as explained in theintroductory portion one can conclude that if the concepts according tothe above embodiment of the invention are used, the loop would be brokenwhen the UE is handed over to WiMAX the second time, because at thatpoint the ANDSF based access selection functionality would have recordedin the 3GPP access preference cache that the 3GPP access selectionfunctionality prefers WCDMA to LTE and since WCDMA according to theANDSF based access selection functionality has lower priority thanWiMAX, there would be no point in handing over the UE to LTE (or anyother access in the 3GPP domain).

It is to be understood, that the features of the above-describedembodiments may also be combined with each other as appropriate.

The concepts according to the above embodiments of the invention wouldtypically be implemented in the ueANDSF, i.e. in the ANDSF based accessselection functionality in the UE, but implementation in the networkbased part of the ANDSF functionality or an implementation distributedbetween the UE and the network is also conceivable, depending on how theoverall responsibilities for the access selection process are dividedbetween the UE based and network based parts of the ANDSF functionality.

It is to be understood that the result of an access selection by any ofthe described access selection functions in any of the above-describedembodiments typically is a particular access network (e.g. a RAN), orpossibly multiple access networks in case of simultaneous multi-access,for a UE in active mode. Further, access selection results in terms ofaccess network discovery instructions, guidelines or recommendations mayindicate one or more particular access networks to scan for or one ormore access technologies to scan for.

Abbreviations

3GPP 3^(rd) Generation Partnership Project

3GPP2 3^(rd) Generation Partnership Project 2 (The standardization bodystandardizing CDMA2000.)

AAA Authentication, Authorization and Accounting

AN Access Network

ANDSF Access Network Discovery and Selection Function

CDMA Code Division Multiple Access

CDMA2000 Cellular network standard based on CDMA

DSMIPv6 Dual-Stack Mobile IPv6

EDGE Enhanced Data rates for GSM Evolution

ePDG Evolved Packet Data Gateway

EPS Evolved Packet System

E-UTRA Evolved Universal Terrestrial Radio Access

E-UTRAN Evolved Universal Terrestrial Radio Access Network

GERAN GSM EDGE Radio Access Network

GPRS General Packet Radio Service

GSM Global System for Mobile communication

hANDSF Home ANDSF (ANDSF functionality in the home network)

hPCRF Home PCRF (PCRF in the home network)

HPLMN Home Public Land Mobile Network

HSPA High Speed Packet Access

HSS Home Subscriber Server

IMS IP Multimedia Subsystem

IP Internet Protocol

IPv4 Internet Protocol version 4

IPv6 Internet Protocol version 6

LTE Long Term Evolution

MIPv4 Mobile IPv4

MIPv6 Mobile IPv6

MME Mobility Management Entity

MS Mobile Station

n3aANDSFANDSF functionality in a non-3GPP access network.

NAS Non-Access Stratum

PAN Personal Area Network

PCE Packet Core Evolution

PCR Packet Core Research

PCRF Policy and Charging Rules Function

P-CSCF Proxy Call Session Control Function

PDN Packet Data Network

PLMN Public Land Mobile Network

PMIPv4 Proxy Mobile IPv4

PMIPv6 Proxy Mobile IPv6

PSS Packet Switched Streaming Service

RAN Radio Access Network

RAT Radio Access Technology

RRC Radio Resource Control

SAE System Architecture Evolution

SGSN Serving GPRS Support Node

SIM Subscriber Identity Module

TS Technical Specification

UE User Equipment

ueANDSF ANDSF functionality in the UE.

UN User Network

USIM Universal Subscriber Identity Module

UTRAN Universal Terrestrial Radio Access Network

vANDSF Visited ANDSF (ANDSF functionality in the visited network)

vPCRF Visited PCRF (PCRF in the visited network)

VPLMN Visited Public Land Mobile Network

WCDMA Wideband Code Division Multiple Access

WiMAX Worldwide Interoperability for Microwave Access

WLAN Wireless Local Area Network

The invention claimed is:
 1. A method of access network selection in amulti-access network environment with one or more 3^(rd) GenerationPartnership Projection (3GPP) access networks and one or more non-3GPPaccess networks to which user equipment directly connect in order toaccess another network, the method comprising the following stepsimplemented by an entity in the environment that has one or moreprocessors: determining preferences with which a 3GPP access selectionfunction selects a 3GPP access network from said one or more 3GPP accessnetworks; and as part of implementing at least a portion of an AccessNetwork Discovery and Selection Function (ANDSF), selecting based onsaid preferences an access network from among said one or more 3GPPaccess networks and said one or more non-3GPP networks.
 2. The method ofclaim 1, wherein the 3GPP access selection function is implemented on adifferent time scale and/or interface than the ANDSF.
 3. The method ofclaim 1, wherein selecting based on said preferences comprises selectinga 3GPP access network only if no other available 3GPP access network ismore preferred by the 3GPP access selection function.
 4. The method ofclaim 1, wherein determining said preferences comprises determining afirst 3GPP access network that is selected by the 3GPP access selectionfunction, and wherein selecting based on said preferences comprisesfiltering out, from the access networks from which the ANDSF selects,those 3GPP access networks that the 3GPP first access selection functionprefers less than said first 3GPP access network.
 5. The method of claim1, wherein determining said preferences comprises determining the accessnetwork selected by the 3GPP access network selection function as beingthe most preferred among those 3GPP access networks that are currentlyavailable.
 6. The method of claim 1, wherein determining saidpreferences comprises obtaining a list of 3GPP access networks orderedaccording to the preferences with which the first 3GPP access selectionfunction selects them.
 7. The method of claim 1, wherein determiningsaid preferences comprises tracking how the user equipment is directedbetween different 3GPP access networks.
 8. The method of claim 7,wherein said tracking comprises, responsive to the user equipment beingdirected from a first 3GPP access network to a second non-3GPP accessnetwork, identifying particular circumstances that currently exist andrecording that the first 3GPP access network is the preferred accessnetwork of the 3GPP access selection function under those particularcircumstances.
 9. The method of claim 8, wherein selecting based on saidpreferences comprises: determining if said particular circumstancesstill currently exist; and if the particular circumstances stillcurrently exist and the first 3GPP access network is available,selecting the first 3GPP access network as long as the ANDSF prefers thefirst 3GPP access network over any available non-3GPP access network,even if the ANDSF prefers a different 3GPP access network over the first3GPP access network.
 10. The method of claim 8, wherein identifying saidparticular circumstances comprises identifying which of said one or more3GPP access networks are currently available.
 11. The method of claim 8,wherein identifying said particular circumstances comprises identifyingwhich applications are currently active on the user equipment.
 12. Themethod of claim 8, wherein identifying said particular circumstancescomprises identifying at least one of: a current geographic location ofthe user equipment; a current velocity of the user equipment; a publicland mobile network at which the user equipment is currently registered;a current time of day; and a current day of the week.
 13. An entity in amulti-access network environment with one or more 3^(rd) GenerationPartnership Projection (3GPP) access networks and one or more non-3GPPaccess networks to which user equipment directly connect in order toaccess another network, the entity comprising: a processor and a memory,said memory containing instructions executable by said processor wherebysaid entity is configured to: determine preferences with which a 3GPPaccess selection function selects a 3GPP access network from said one ormore 3GPP access networks; and as part of implementing at least aportion of an Access Network Discovery and Selection Function (ANDSF),select based on said preferences an access network from among said oneor more 3GPP access networks and said one or more non-3GPP networks. 14.The entity of claim 13, wherein the 3GPP access selection function isimplemented on a different time scale and/or interface than the ANDSF.15. The entity of claim 13, wherein said memory contains instructionsexecutable by said processor whereby said entity is configured to selecta 3GPP access network only if no other available 3GPP access network ismore preferred by the 3GPP access selection function.
 16. The entity ofclaim 13, wherein said memory contains instructions executable by saidprocessor whereby said entity is configured to: determine a first 3GPPaccess network that is selected by the 3GPP access selection function,and filter out, from the access networks from which the ANDSF selects,those 3GPP access networks that the 3GPP access selection functionprefers less than said first 3GPP access network.
 17. The entity ofclaim 13, wherein said memory contains instructions executable by saidprocessor whereby said entity is configured to determine the accessnetwork selected by the 3GPP access network selection function as beingthe most preferred among those 3GPP access networks that are currentlyavailable.
 18. The entity of claim 13, wherein said memory containsinstructions executable by said processor whereby said entity isconfigured to obtain a list of 3GPP access networks ordered according tothe preferences with which the 3GPP access selection function selectsthem.
 19. The entity of claim 13, wherein said memory containsinstructions executable by said processor whereby said entity isconfigured to track how the user equipment is directed between different3GPP access networks.
 20. The entity of claim 19, wherein said memorycontains instructions executable by said processor whereby said entityis configured, responsive to the user equipment being directed from afirst 3GPP access network to a second non-3GPP access network, toidentify particular circumstances that currently exist and record thatthe first 3GPP access network is the preferred access network of the3GPP access selection function under those particular circumstances. 21.The entity of claim 20, wherein said memory contains instructionsexecutable by said processor whereby said entity is configured to:determine if said particular circumstances still currently exist; and ifthe particular circumstances still currently exist and the first 3GPPaccess network is available, select the first 3GPP access network aslong as the ANDSF prefers the first 3GPP access network over anyavailable non-3GPP access network, even if the ANDSF prefers a different3GPP access network over the first 3GPP access network.
 22. The entityof claim 13, wherein the entity is said user equipment.
 23. A computerprogram product stored on a non-transitory computer readable medium andcomprising program code that when executed on a processor of an entityin a multi-access network environment controls the entity to performaccess network selection, the multi-access networks having one or more3^(rd) Generation Partnership Projection (3GPP) access networks and oneor more non-3GPP access networks to which user equipment directlyconnect in order to access another network, the program code causing theentity to: determine preferences with which a 3GPP access selectionfunction selects a 3GPP access network from said one or more 3GPP accessnetworks; and as part of implementing at least a portion of an AccessNetwork Discovery and Selection Function (ANDSF), select based on saidpreferences an access network from among said one or more 3GPP accessnetworks and said one or more non-3GPP networks.